Abstract 1024: The challenge of standardizing the measurement of an imprecise biomarker like HRD

Abstract

Here we present data on the characterization and implementation of a set of reference materials for the standardization of homologous recombination deficiency (HRD) assessment. The safety and effectiveness profile of a drug can be improved by using it in patients where that drug is most likely to be effective. While PARP inhibitors are indicated for use in some patients with ovarian, breast, pancreatic, and prostate cancer, patients with other cancers that are deficient in homologous recombination repair (HRR) might also benefit from their use. However, determining whether a cancer is HRD-positive is neither trivial nor precise. While clinical trials have shown that patients with deleterious mutations in BRCA2 and BRCA1 are most likely to benefit from PARP inhibitors, determining that a given BRCA mutation (or set of such mutations) is in fact deleterious is frequently not straightforward. Therefore, assays are now looking for signs of HRD, such as genomic instability consistent with non-homologous end joining (NHEJ) being used for the repair of double-stranded breaks in DNA as opposed to HRR. For example, some assays look at the combination of loss of heterozygosity (LOH) and large-scale state transitions (LST) across chromosomes as well as telomeric allelic imbalance (TAI) when determining whether a cancer is HRD-positive, while other assays use alternative approaches. How those characteristics are measured, integrated, and distilled into a final determination of whether HRD is present or absent varies, which can create uncertainty around treatment options and enrollment into clinical trials. This also makes the path of follow-on companion diagnostics challenging because perfect agreement between imprecise measurements is unlikely. In order to enable more standardized reporting of HRD and to enable the assessment of HRD assays, we created a set of characterized reference materials composed of HRD negative, borderline, and positive tumor/normal matched cell lines that were analyzed using both array-based and next generation sequencing-based assays in order to characterize chromosomal changes across their genomes and obtain HRD scores. Because of differences in the results, assay imprecision should be taken into account in clinical trials that implement cutoffs in order to establish safety data for patients who are biomarker-negative but may be biomarker-positive in a future assay, which is similar to what is done for complementary diagnostics. Citation Format: Yves Konigshofer, Matthew G. Butler, Krystyna Nahlik, Dana Ruminski Lowe, Catherine Huang, Omoshile Clement, Russell K. Garlick. The challenge of standardizing the measurement of an imprecise biomarker like HRD [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1024.